Microelectronic circuits use metal films or layers for a wide range of purposes. For example, metal layers may be used to electrically interconnect the various components on a workpiece, such as the components formed in a semiconductor wafer. Further, the metal layers may be used to form the actual electronic components on the workpiece. The metal layers are typically applied onto the wafer in an electroplating processor.
Electroplating involves immersing an electrically conductive surface, such as a metal seed layer, on the device side of the wafer into a plating bath. The electrically conductive surface forms a current path between an immersed electrode and electrical contacts touching the electrically conductive surface around the edge of the wafer. Metal is deposited on the workpiece from the electrolyte (electroplating) or removed from the workpiece (electropolishing/etching), depending on the direction of the current flow.
Terminal effects resulting from non-uniform current flow at the edges of the wafer, and the irregular geometry of the wafer edge, can cause non-uniform plating at the edges of the wafer. Accordingly, metal plated onto the edges of the wafer is more prone to breaking or flaking off of the wafer, creating contaminant particles. Semiconductor wafers are also generally handled or supported by their edges. Hence, metal plated onto the wafer at the wafer edges can be a serious source of potential contamination. For these reasons, electroplating metal at the edges is generally avoided. In practice, an annular seal in the head of the electroplating processor is typically held against the wafer during electroplating, to seal the plating bath liquid away from the wafer edges. After electroplating, the seal is moved away from the wafer, or vice versa. However, in some cases, the wafer may tend to stick to the seal. This creates risk of damage to the wafer, and can also slow the manufacturing process. Accordingly, improvements in wafer handling in electroplating processing are needed.